The invention generally relates to a regulating the communication of power to components of a fuel cell system.
A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a polymer electrolyte membrane (PEM), often called a proton exchange membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:H2→2H++2e− at the anode of the cell, andO2+4H++4e−→2H2O at the cathode of the cell.
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide more power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. Electrically conductive gas diffusion layers (GDLs) may be located on each side of each PEM to form the anode and cathodes of each fuel cell. In this manner, reactant gases from each side of the PEM may leave the flow channels and diffuse through the GDLs to reach the PEM.
The powering up of the fuel cell system must be carefully regulated, especially in view of the various stray gases that may be present. In this manner, the fuel cell system must be powered up in a manner to ensure that if significant levels of certain stray gases (hydrogen, for example) are present, these levels are reduced before electricity is provided to components of the fuel cell system. Otherwise, a hazardous condition may result, as an electrical spark may ignite a stray gas.
The presence of significant stray gas levels inside the compartment is an example of one of the various alarm conditions that need to be monitored in connection with operation of the fuel cell system. Thus, the fuel cell system typically include various sensors for purposes of detecting these alarm conditions. In this manner, should a sensor in the fuel cell compartment indicate an unacceptable level of a particular stray gas or another alarm condition (such as an over temperature condition or an over pressure condition (as examples)) during power up or at any other time, corrective action may need to be taken.
Thus, there is a continuing need for better techniques and arrangements to control the delivery of power to components of the fuel cell system.